The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Some powertrain control systems estimate the grade of a road on which a vehicle is traveling and control an engine and a transmission based on the estimated road grade. For example, under normal conditions, a powertrain control system may automatically stop the engine when the engine is idling and automatically restart the engine when a brake pedal is released or an accelerator pedal is applied. However, when the estimated road grade is greater than a predetermined grade, indicating that the vehicle is on a steep hill, the powertrain control system may refrain from automatically stopping the engine. In another example, the powertrain control system may adjust a transmission shift pattern based on the estimated road grade.
The road grade is typically estimated using a relationship such as
                              sin          ⁢                                          ⁢          α                =                                            F              g                                      F              α                                =                                    ma              g                                      F              α                                                          (        1        )            where α is the road grade, Fg is the force acting on the vehicle due to gravity, Fα is the force acting on the vehicle due to the road grade, m is the mass of the vehicle, and ag is the acceleration of the vehicle due to gravity. The mass of the vehicle may be predetermined based on an assumed number of passengers and an assumed payload. The acceleration of the vehicle due to gravity may be a predetermined value (e.g., 9.8 meters per seconds squared).
The force acting on a vehicle due to the road grade is typically estimated using a relationship such asΣF=FENG+FAD+Fα=maL  (2)where ΣF is a sum of the longitudinal forces acting on the vehicle, FENG is the force acting on the vehicle due to the torque output of the engine, FAD is the aerodynamic force acting on the vehicle, Fα is the force acting on the vehicle due to the road grade, m is the mass of the vehicle, and aL is the longitudinal acceleration of the vehicle. The force acting on the vehicle due to the torque output of the engine may be estimated based on measured engine operating conditions. The aerodynamic force acting on the vehicle may be estimated based on an assumed wind force. The longitudinal acceleration of the vehicle may be determined based on a measured vehicle speed.
Powertrain control systems typically assume that a vehicle is moving when estimating the torque output of an engine in the vehicle based on engine operating conditions. In addition, the relationship typically used to estimate the force acting on a vehicle due to the road grade does not account for the force acting on the vehicle due to braking. Thus, if a vehicle is stopped or if a brake is applied, the powertrain control systems typically do not estimate the road grade due to potential inaccuracies in the estimated road grade. Further, even when the vehicle is moving and the brake is not applied, the estimated road grade may be inaccurate due to other assumptions made when estimating the road grade. These other assumptions may include the assumed number of passengers, the assumed payload, and//or the assumed wind force.
Inaccuracies in the estimated road grade may adversely affect the ability of a powertrain control system to control an engine and a transmission based on the estimated road grade. For example, the estimated road grade may falsely indicate that a vehicle is on a steep hill. Therefore, the powertrain control system may not automatically stop an engine when the engine is idling as desired, which may adversely affect fuel economy.